The present invention relates to a gear designed, so that a rotational-power transmitting member can be fitted into a gear body, whereby a power can be transmitted through such member to a desired device, and more particularly, a gear in which a shock force produced at the start and stoppage of the rotation of the gear can be moderated to reduce a noise during rotation of the gear, while reducing the number of parts, the number of operations and the cost which are required for producing the gear.
This type of the conventional gear is conventionally comprised of a rim integral with a plurality of teeth at an outer peripheral surface thereof, a boss disposed concentrically inside the rim, and a plurality of ribs disposed radiately between the rim and the boss and connected at their opposite ends to the rim and the boss. The rim, the boss and the ribs are integrally formed in the gear, and fitting sections are provided between the boss and the rim, so that the rotational power of a gear body can be transmitted to the disk-shaped rotational-power transmitting member, while a predetermined amount of a shock generated with the rotation of the gear body, by fitting a portion of a disk-shaped rotational-power transmitting member to the fitting sections.
A conventional example of this type of the gear is shown in FIG. 1. The gear body 10 includes teeth 11, a rim 12, a boss, a web 14 and ribs 15. The cylindrical rim 12 is integral with the plurality of teeth 11 at its outer peripheral surface. The boss 13 is disposed concentrically with the rim 12. The rim 14 is connected to the rim 12 and the boss 13. The plurality of ribs 15 extend radiately from the boss 13 toward the rim 12 and is connected to the outer peripheral surface of the boss 13, the inner peripheral surface of the rim 12 and the web 14. The teeth 11, the rim 12, the boss 13 and the web 14 are integrally formed by pouring a molten material comprising a synthetic resin into a mold.
The fitting sections 16 are formed separately from the rim 12, the boss 13, the web 14 and the ribs 15, using a rubber which is soft as compared with the synthetic resin for forming the gear body. The fitting sections 16 are partitioned by the ribs 15; smoothly or tightly inserted in spaces defined in the gear body 10 by the rim 12, the boss 13 and the web 14; and fixed using a fixing means such as a screw which is not shown, or an adhesive.
A notch or recess 16a is defined in each of the fitting sections 16, so that a disk-shaped rotational-power transmitting member can be fitted in the notch or recess 16a. 
One example of the disk-shaped power transmitting member is shown in FIG. 2. The disk-shaped power transmitting member 17 has projections 17a provided on one side thereof and each having such a shape that the projections 17a can be fitted into the notches or recessed 16a of the fitting sections 16 mounted to the gear shown in FIG. 1. Thus, the disk-shaped power transmitting member 17 is adapted to be rotated coaxially with the gear by fitting the projections 17a into the notches or recesses 16a. 
A shaft 17b is provided on the other side of the disk-shaped power transmitting member 17. The shaft 17b is formed into, for example, a rectangular box-shape as shown in FIG. 2, or as a serration shaft, so that any of various power transmitting members such as various gears and, pulleys can be connected to the shaft 17b. 
Thus, when the gear body 10 is rotated, the rotational force thereof is transmitted through the fitting sections 16 to the disk-shaped rotational-power transmitting member 17 to rotate the rotational-power transmitting member 17, and further, the rotational power of the power transmitting member 17 is transmitted to another power transmitting member.
Now, when the rotation of the gear is started, and when the rotation is stopped, an excessive load is applied to the teeth of the gear and the disk-shaped rotational-power transmitting member 17 rotated along with the gear. For this reason, there is a possibility that the meshing of the teeth is degraded, and the loudness of a noise produced during rotation of the gear is increased and in its turn, an adverse affection is exerted to the life of the gear.
Therefore, in the conventional gear of this type, a fitting section 16 made of a rubber separately from the gear body is mounted to the gear body to function as a buffering member for absorbing a shock produced with the rotation of the gear by the elastic deformation of the fitting portion 16, thereby improving the meshing of the teeth of the gear for a period from the start of the rotation of the gear to the stoppage of the rotation to reduce the noise generated during rotation of the gear.
However, when a buffering member made of a rubber separately from a gear body is mounted to the gear body as in the conventional gear, the number of parts are increased correspondingly and moreover, the operation for mounting the buffering member is complicated; the labor required for producing the gear is increased; the efficiency for producing the gear is lowered; and the producing cost is increased. In addition, when buffering member made of the rubber separately from the gear body is mounted to the gear body, there is a possibility that an operator may forget the mounting of the buffering member, and it is difficult to enhance the yield of a product having a good quality. When a buffering member made of a rubber is not mounted to the gear body, and a recess, into which a projection of a disk-shaped rotational-power transmitting member can be fitted, is defined directly in the gear body, an excessive shock produced at the start and stoppage of the rotation of the gear is transmitted, as it is, to the disk-shaped rotational-power transmitting member and the gear body and as a result, the meshing of the teeth of the gear is degraded, and the noise generated with the rotation of the gear cannot be reduced.
Accordingly, it is an object of the present invention to provide a gear wherein the labor for mounting the buffering member made of the rubber to the gear body can be eliminated, thereby enhancing the efficiency of production of the gear and reducing the producing cost.
To achieve the above object, according to the present invention, there is provided a gear comprising a gear body which includes a rim integral with a plurality of teeth at an outer peripheral surface thereof, and a boss disposed concentrically inside the rim, and at least one fitting section which is formed from a material having a low hardness and a low flexural strength as compared with a material for forming the gear body and which is provided between the rim and the boss, so that the gear with a rotational-power transmitting member fitted into the fitting portion is rotated, whereby the rotational power of the gear body is transmitted to the rotational-power transmitting member, while elastically deforming the fitting section to absorb a predetermined amount of a shock produced with the rotation of the gear body, wherein the gear body and the fitting section are formed integrally with each other by a two-color molding process.
Preferably, the fitting section is formed to fill a space which is comprised of a recess defined by at least the rim, the boss and a web formed between the boss and the rim, and a bore portion communicating with the bottom surface of the recess and defined into such a shape that the sectional area at a predetermined location spaced apart from the bottom surface of the bore portion is larger than the sectional area at a location of connection to the bottom surface of the recess.
Preferably, the bore portion comprises a groove defined in the web on the opposite side from the side in which the recess is defined, and a through-bore having a sectional area smaller than the sectional area of the bottom surface of any of the recess and the groove.
Preferably, the bore portion comprises a through-bore or a groove which communicates with the recess and which is defined into such a tapered shape that the sectional area is increased gradually in a direction from the bottom surface of the recess toward a deeper portion thereof.
Preferably, the side face of the recess is formed into such a tapered shape that the sectional area is increased gradually toward the bottom surface.
Preferably, the gear body is formed from a high-rigid synthetic resin by an injection molding, and the fitting section is formed from a thermoplastic elastomer by an injection molding.
With the gear formed in the above manner according to the present invention, it is unnecessary to produce a buffering member made of a rubber separately from the gear body and to mount the buffering member to the gear body, as in the conventional gear and hence, the number of part and the number of producing steps required for producing the gear can be decreased to reduce the producing cost. In addition, the buffering section cannot be separated from the gear body, leading to an enhanced quality of a gear product.
It is another object of the present invention to provide a gear wherein an excessive shock produced with the rotation of the gear can be absorbed without mounting of a buffering member made of a rubber to the gear body, thereby improving the meshing of teeth of the gear and reducing the noise.
To achieve the above object, according to the present invention, there is provided a gear comprising a gear body which is formed, so that a rotational-power transmitting member is fitted into the gear body to transmit a power through the rotational-power transmitting member, wherein the gear further includes at least one fitting section into which the rotational-power transmitting member can be fitted, and which is formed integrally on the gear body into an elastically deformable shape.
Preferably, the gear body comprises a rim integral with a plurality of teeth at its outer peripheral surface, a boss disposed concentrically inside the rim, and a plurality of ribs disposed radiately between the rim and the boss, and a plurality of the fitting sections are provided in areas partitioned between the boss and the rim by the ribs for fitting the disk-shaped rotational-power transmitting member into the gear body, each of the fitting sections being formed integrally in the gear body into such a shape that it can be elastically deformed along a web formed between the rim and the boss.
Preferably, the fitting section is connected at least at one end thereof to either one of the boss, the rim, the ribs and the web. At least most of that face of the fitting section, which is turned toward the web, is comprised of one or more elastic deformable portion which is formed so that it is not connected to the web.
Preferably, each of the fitting sections is formed, so that a projection provided on the rotational-power transmitting member is damped by the two or more elastic deformable portions.
Preferably, the elastic deformable portion includes an area having a folded shape or an area having a curved shape.
With the gear formed in the above manner according to the present invention, a shock generated with the rotation of the gear can be absorbed by the gear body itself without use of a buffering member made of a rubber used in the conventional gear. Therefore, according to the present invention, it is possible to reduce a noise and an error of meshing of the teeth produced during rotation of the gear to an extent equivalent to or more than that in the conventional gear including the buffering member made of a rubber.
It is a further object of the present invention to provide a gear wherein a rotational power can be transmitted to a power transmitting member connected to the gear, while absorbing an excessive shock generated with the rotation of the gear without mounting of a disk-shaped rotational-power transmitting member and a buffering member made of a rubber to a gear body to improve the meshing of the teeth of the gear and to reduce the noise, thereby reducing the number of parts, the number of operating steps and the producing cost, which are required for producing the gear.
To achieve the above object, according to the present invention, there is provided a gear comprising a rim integral with a plurality of teeth at its outer peripheral surface, a boss disposed concentrically inside the rim, and a plurality of elastically deformable ribs disposed radiately between the rim and the boss, the rim and the boss being connected to each other by the plurality of ribs.
With the gear formed in the above manner according to the present invention, it is possible to remarkably reduce the number of parts, the number of operating steps and the producing cost, which are required for producing the gear, while reducing the noise generated during rotation of the gear to an extent more than that in the conventional gear including the buffering member made of the rubber and the disk-like rotational-power transmitting member.
The above and other objects, features and advantages of the invention will become apparent from the following description of the preferred embodiment taken in conjunction with the accompanying drawings.